Hi all, I have Win 2000 advanced server ?with SP2- Domain Controller which used as Exchange 2000 server for Instant messaging service, and I have other Windows 2000 advanced server ?with SP2- ( member of domain ) which used as ISA server 2000 for web sharing used. The problem is: As usual if I want the client to connect to the Internet through the ISA server I must configure the proxy setting in the Internet Browser ( for example Internet Explorer ) by check the option USE A PROXY SERVER on LAN Setting and put the address =[ISA server IP address] and the port =[ 8080]. When I do that, the Messenger application will be not working with the error INSTANT MESSAGING AUTHINTICATION ERROR, but when I clear the option ( USE A PROXY SERVER ) from the Internet explorer browser setting ,the Instant messaging works but sure the Internet will be stop . Please any help.